The present invention relates to a timer for measuring a time interval, for instance, by counting clock pulses, and more particularly to a time interval measuring instrument which measures a time interval, with high accuracy, by expanding a fraction of the clock period to thereby compensate for drift and nonlinearity.
For the measurement of a time interval .DELTA.T that is desired to be obtained, a time interval equivalent to an addition of .DELTA.T and a constant nT.sub.0 (n being a positive integer and T.sub.0 a fixed value) is measured after being expanded at a fixed rate, and constant time intervals (n+1)T.sub.0 and nT.sub.0 are respectively measured after similarly being expanded at the abovesaid fixed rate. The following expression is calculated using the measured results of the time intervals .DELTA.T+nT.sub.0, (n+1)T.sub.0 and nT.sub.0 : ##EQU2##
Such interval expansion measurements can be achieved with high accuracy. In addition, by expanding the time interval added with the fixed value nT.sub.0 as described above, a linear expansion can be done even though the time interval .DELTA.T is very short and even though the expansion characteristic of the interval expanding means is nonlinear in a small input time interval region. Furthermore, even if a temperature drift exists in the expanding means, the drift component is removed by the calculation of the abovementioned expression, ensuring accurate measurement. Such a time interval measuring instrument is disclosed in U.S. Pat. No. 4,267,436 entitled "Interval-Expanding Timer Compensated for Drift and Nonlinearity", issued on May 12, 1981. According to the interval expanding means set forth in this U.S. patent, the aforesaid time intervals .DELTA.T.sub.1 +nT.sub.0, (n+1)T.sub.0 and nT.sub.0 are respectively converted by a common integrator into voltages, which are held in individual voltage hold circuits. Coincidence is detected between each of the voltages held in the hold circuits and the integrated output from an integrator lower in integration rate than the abovesaid integrator, and the period of time from the start of integration by the latter integrator to the detection of coincidence is yielded as an output of the expanded time interval. In the prior art, for the three voltages, hold circuits are employed as referred to above, and dispersion in their characteristics due to temperature variations and aging introduces errors in measurement.
It is therefore an object of the present invention to provide a time interval measuring instrument which is insusceptible to the influence of ambient temperature change and aging.
Another object of the present invention is to provide a time interval measuring instrument which permits simplification of the arrangement of a controller and other circuits in the instrument.